Equine grass sickness is associated with major abnormalities in the ultrastructure of skeletal neuromuscular junctions.

BACKGROUND: Equine grass sickness (EGS) is a frequently fatal multisystem neuropathy of equids. The aetiology is unknown; proposed causes include toxicoinfection with Clostridium botulinum and a mycotoxicosis. The effect of EGS on the organisation and structural integrity of the skeletal neuromuscular junction (NMJ), the target of botulinum neurotoxins (BoNTs), is unknown. OBJECTIVES: To compare the organisation and structural integrity of skeletal NMJs from EGS horses, control horses and one horse with a presumptive diagnosis of botulism. STUDY DESIGN: Blinded, retrospective case control. METHODS: NMJs in samples of diaphragm or intercostal muscle from six EGS horses, three control horses and one equine botulism case were compared using electron microscopy, morphometry and confocal light microscopy. RESULTS: A significantly higher percentage of EGS NMJs had abnormal morphology (EGS 72.2%, 95% CI 55.6-84.4; Controls 6.9%, 1.7-23.8; OR 35.1, 8.47-244.8; p < 0.001). EGS NMJs had a significantly lower mean volume fraction occupied by synaptic vesicles (SVs) (EGS 18.7%, 12.6-28.0; Controls 36.3%, 20.8-63.4; p = 0.024). EGS NMJs had evidence of accelerated SV exocytosis and SV depletion, accumulation of neurofilament-like material in terminal boutons and/or bouton degeneration. NMJs from the botulism horse had dense packing of SVs towards the presynaptic membrane active zone, consistent with BoNT intoxication, but had absence of the abnormalities identified in EGS NMJs. MAIN LIMITATIONS: Group sizes were limited by difficulties obtaining suitably processed samples. Ages of control and EGS horses differed. Botulism was diagnosed based on clinical and post mortem findings. CONCLUSIONS: EGS is associated with major changes in skeletal NMJ ultrastructure that are inconsistent with the effects of BoNTs. SV depletion may reflect increased exocytosis coupled with reduced repopulation of SVs via anterograde axonal transport and endocytosis, consistent with the action of an excitatory presynaptic toxin and/or neurotransmitter reuptake inhibitor. Skeletal NMJs represent a previously unrecognised target for the toxin that causes EGS.

Lesser weever fish (Echiichthys vipera Cuvier, 1829) venom is cardiotoxic but not haemorrhagic.

Despite comprising over half of the biodiversity of living venomous vertebrates, fish venoms are comparatively understudied. Venom from the lesser weever fish (Echiichthys vipera syn. Trachinus vipera) has received only cursory attention despite containing one of the most potent venom toxins (trachinine). Literature records are further complicated by early studies combining the venom with that of the related greater weever (Trachinus draco). The current study used a chicken chorioallantoic membrane assay to investigate venom bioactivity following the application of measured quantities of crude venom to a major bilateral vein at 1 cm distance from the heart. The venom had a dose-dependent effect on survival rate and exhibited dose-dependent cardiotoxic properties at day six of development. Crude E. vipera triggered tachycardia at doses of 37.58 and 44.88 µg/µL and bradycardia at 77.4 µg/µL. The three highest doses (65.73, 77.4 and 151.24 µg/µL) caused significant mortality. These data also suggested intra-specific variation in E. vipera venom potency. Unlike a number of other piscine venoms, E. vipera venom was not haemorrhagic at the concentrations assayed.

The venoms of the lesser (Echiichthys vipera) and greater (Trachinus draco) weever fish- A review.

In comparison with other animal venoms, fish venoms remain relatively understudied. This is especially true for that of the lesser Echiichthys vipera and greater weever fish Trachinus draco which, apart from the isolation of their unique venom cytolysins, trachinine and dracotoxin, respectively, remain relatively uncharacterised. Envenomation reports mainly include mild symptoms consisting of nociception and inflammation. However, like most fish venoms, if the venom becomes systemic it causes cardiorespiratory and blood pressure changes. Although T. draco venom has not been studied since the 1990's, recent studies on E. vipera venom have discovered novel cytotoxic components on human cancer cells, but due to the scarcity of research on the molecular make-up of the venom, the molecule(s) causing this cytotoxicity remains unknown. This review analyses past studies on E. vipera and T. draco venom, the methods used in the , the venom constituents characterised, the reported symptoms of envenomation and compares these findings with those from other venomous Scorpaeniformes.

The importance of being genomic: Non-coding and coding sequences suggest different models of toxin multi-gene family evolution.

Studies of multi-gene protein families, including many toxins, are crucial for understanding the role of gene duplication in generating protein diversity in general. However, many evolutionary analyses of gene families are based on coding sequences, and do not take into account many potentially confounding evolutionary factors, such as recombination and convergence due to selection. We illustrate this using snake venom gene sequences from the Phospholipase A2 (PLA2) subfamily. Novel gene sequences from 20 species of understudied Asian pitvipers were analyzed alongside available genomic PLA2 sequences from another four crotaline and several viperine species. In contrast to previous analyses of this toxin family based on cDNA sequences, we find that duplication events are concentrated at the tips of the tree, suggesting that major functions such as presynaptic neurotoxicity have evolved convergently multiple times in pitvipers. We provide evidence that this discrepancy is due to differing evolutionary patterns between introns and exons. The effects of several well-known sources of bias on the phylogeny were small, compared to the effect of analyses based on different partitions of the gene (whole gene sequence, non-coding regions, cDNA sequence). Switches of function were found to be largely associated with strong selection, and with duplication events. Use of coding sequences for phylogeny estimation potentially produces incorrect inferences about the action of selection on individual lineages and sites. Our results have major implications for phylogenomic methods of functional inference as well as for our understanding of the evolution of multigene families.

Secreted phospholipases A2 of snake venoms: effects on the peripheral neuromuscular system with comments on the role of phospholipases A2 in disorders of the CNS and their uses in industry.

Neuro- and myotoxicological signs and symptoms are significant clinical features of envenoming snakebites in many parts of the world. The toxins primarily responsible for the neuro and myotoxicity fall into one of two categories--those that bind to and block the post-synaptic acetylcholine receptors (AChR) at the neuromuscular junction and neurotoxic phospholipases A2 (PLAs) that bind to and hydrolyse membrane phospholipids of the motor nerve terminal (and, in most cases, the plasma membrane of skeletal muscle) to cause degeneration of the nerve terminal and skeletal muscle. This review provides an introduction to the biochemical properties of secreted sPLA2s in the venoms of many dangerous snakes and a detailed discussion of their role in the initiation of the neurologically important consequences of snakebite. The rationale behind the experimental studies on the pharmacology and toxicology of the venoms and isolated PLAs in the venoms is discussed, with particular reference to the way these studies allow one to understand the biological basis of the clinical syndrome. The review also introduces the involvement of PLAs in inflammatory and degenerative disorders of the central nervous system (CNS) and their commercial use in the food industry. It concludes with an introduction to the problems associated with the use of antivenoms in the treatment of neuro-myotoxic snakebite and the search for alternative treatments.

Predicting function from sequence in a large multifunctional toxin family.

Venoms contain active substances with highly specific physiological effects and are increasingly being used as sources of novel diagnostic, research and treatment tools for human disease. Experimental characterisation of individual toxin activities is a severe rate-limiting step in the discovery process, and in-silico tools which allow function to be predicted from sequence information are essential. Toxins are typically members of large multifunctional families of structurally similar proteins that can have different biological activities, and minor sequence divergence can have significant consequences. Thus, existing predictive tools tend to have low accuracy. We investigated a classification model based on physico-chemical attributes that can easily be calculated from amino-acid sequences, using over 250 (mostly novel) viperid phospholipase A2 toxins. We also clustered proteins by sequence profiles, and carried out in-vitro tests for four major activities on a selection of isolated novel toxins, or crude venoms known to contain them. The majority of detected activities were consistent with predictions, in contrast to poor performance of a number of tested existing predictive methods. Our results provide a framework for comparison of active sites among different functional sub-groups of toxins that will allow a more targeted approach for identification of potential drug leads in the future.

A role for solvents in the toxicity of agricultural organophosphorus pesticides.

Organophosphorus (OP) insecticide self-poisoning is responsible for about one-quarter of global suicides. Treatment focuses on the fact that OP compounds inhibit acetylcholinesterase (AChE); however, AChE-reactivating drugs do not benefit poisoned humans. We therefore studied the role of solvent coformulants in OP toxicity in a novel minipig model of agricultural OP poisoning. Gottingen minipigs were orally poisoned with clinically relevant doses of agricultural emulsifiable concentrate (EC) dimethoate, dimethoate active ingredient (AI) alone, or solvents. Cardiorespiratory physiology and neuromuscular (NMJ) function, blood AChE activity, and arterial lactate concentration were monitored for 12h to assess poisoning severity. Poisoning with agricultural dimethoate EC40, but not saline, caused respiratory arrest within 30 min, severe distributive shock and NMJ dysfunction, that was similar to human poisoning. Mean arterial lactate rose to 15.6 [SD 2.8] mM in poisoned pigs compared to 1.4 [0.4] in controls. Moderate toxicity resulted from poisoning with dimethoate AI alone, or the major solvent cyclohexanone. Combining dimethoate with cyclohexanone reproduced severe poisoning characteristic of agricultural dimethoate EC poisoning. A formulation without cyclohexanone showed less mammalian toxicity. These results indicate that solvents play a crucial role in dimethoate toxicity. Regulatory assessment of pesticide toxicity should include solvents as well as the AIs which currently dominate the assessment. Reformulation of OP insecticides to ensure that the agricultural product has lower mammalian toxicity could result in fewer deaths after suicidal ingestion and rapidly reduce global suicide rates.

Neuromuscular toxicology of the venom of Collett's snake (Pseudechis colletti): a histopathological study.

INTRODUCTION: A bite by Collett's snake, (Pseudechis colletti) can cause rhabdomyolysis in human victims but no signs of neurotoxicity. The pathology of muscle and peripheral nerve has not been described previously. In this study we investigated neuromuscular toxicity in rats. METHODS: The venom was inoculated subcutaneously into the anterolateral aspect of one hindlimb of adult rats at a dose replicating that inoculated into an adult human male during an envenoming bite. RESULTS: The venom caused edema, an increase in muscle wet weight, and the degeneration of 20-35% of the underlying soleus muscle. Muscle fiber regeneration began at 4 days and was complete by 8 weeks. There was little evidence of either post- or presynaptic toxicity. CONCLUSIONS: The dominant effect of this venom in mammals is myotoxicity.

The greater black krait (Bungarus niger), a newly recognized cause of neuro-myotoxic snake bite envenoming in Bangladesh.

Prospective studies of snake bite patients in Chittagong, Bangladesh, included five cases of bites by greater black kraits (Bungarus niger), proven by examination of the snakes that had been responsible. This species was previously known only from India, Nepal, Bhutan and Burma. The index case presented with descending flaccid paralysis typical of neurotoxic envenoming by all Bungarus species, but later developed generalized rhabdomyolysis (peak serum creatine kinase concentration 29,960 units/l) with myoglobinuria and acute renal failure from which he succumbed. Among the other four patients, one died of respiratory paralysis in a peripheral hospital and three recovered after developing paralysis, requiring mechanical ventilation in one patient. One patient suffered severe generalized myalgia and odynophagia associated with a modest increase in serum creatine kinase concentration. These are the first cases of Bungarus niger envenoming to be reported from any country. Generalized rhabdomyolysis has not been previously recognized as a feature of envenoming by any terrestrial Asian elapid snake, but a review of the literature suggests that venoms of some populations of Bungarus candidus and Bungarus multicinctus in Thailand and Vietnam may also have this effect in human victims. To investigate this unexpected property of Bungarus niger venom, venom from the snake responsible for one of the human cases of neuro-myotoxic envenoming was injected into one hind limb of rats and saline into the other under buprenorphine analgesia. All animals developed paralysis of the venom-injected limb within two hours. Twenty-four hours later, the soleus muscles were compared histopathologically and cytochemically. Results indicated a predominantly pre-synaptic action (ß-bungarotoxins) of Bungarus niger venom at neuromuscular junctions, causing loss of synaptophysin and the degeneration of the terminal components of the motor innervation of rat skeletal muscle. There was oedema and necrosis of extrafusal muscle fibres in envenomed rat soleus muscles confirming the myotoxic effect of Bungarus niger venom, attributable to phospholipases A2. This study has demonstrated that Bungarus niger is widely distributed in Bangladesh and confirms the risk of fatal neuro-myotoxic envenoming, especially as no specific antivenom is currently manufactured. The unexpected finding of rhabdomyolysis should prompt further investigation of the venom components responsible. The practical implications of having to treat patients with rhabdomyolysis and consequent acute renal failure, in addition to the more familiar respiratory failure associated with krait bite envenoming, should not be underestimated in a country that is poorly equipped to deal with such emergencies.

Snake bite in Chittagong Division, Bangladesh: a study of bitten patients who developed no signs of systemic envenoming.

The demographics, epidemiology, first aid, clinical management, treatment and outcome of snake bites causing no significant signs of systemic envenoming were documented in Chittagong Medical College Hospital, Bangladesh, between May 1999 and October 2002. Among 884 patients admitted, 350 were systemically envenomed and 534 were without signs of either systemic or significant local envenoming. The average age of patients with physical evidence of snake bite but no systemic envenoming was 26.4 years. Most had been bitten on their feet or hands. Ligatures had been applied proximal to the bite site in >95% of cases and the bite site had been incised in 13%. Patients were typically discharged at 24h. Those with clinical signs of systemic envenoming resembled the non-envenomed cases demographically and epidemiologically except that they arrived at hospital significantly later than non-envenomed patients, having spent longer with traditional healers. No non-envenomed patient was treated with antivenom and none went on to develop symptoms of systemic envenoming after discharge. The potential complications and confusing signs caused by ligatures and incision demand that all patients admitted with a history of snake bite be kept under observation for 24h after admission even if they have no signs of systemic envenoming.

Morphological changes in murine skeletal muscle in response to exercise and mesterolone.

Light and electron microscopy and quantitative morphometry were used to determine the effects of exercise and mesterolone on the soleus muscles of mice. Both exercise and mesterolone caused a significant hypertrophy of extrafusal muscle fibres. The hypertrophy of Type I fibres was greater than that of Type II fibres. There was no hyperplasia. Mitochondria were more numerous and larger than in the muscles of sedentary animals. Capillarity increased and small centrally nucleated muscle fibres appeared, usually in small clusters and most often in the muscles of animals exposed to mesterolone. A small proportion of satellite cells exhibited signs of activation but there were more in the muscles of mesterolone-treated animals than after exercise. Muscles from animals that had been both exercised and treated with mesterolone exhibited the largest changes: muscle mass and muscle fibre hypertrophy was greater than in all other groups of animals, capillarity was higher and >30% of all recognized satellite cells exhibited signs of activation. Groups of small centrally nucleated muscle fibres were commonly seen in these muscles. They appeared to be the result of splits in the form of sprouts from existing muscle fibres. With both exercise and mesterolone, alone or in combination, there was an increase in the proportion of Type I muscle fibres and a decrease in the proportion of Type II.

Identity, developmental restriction and reactivity of extralaminar cells capping mammalian neuromuscular junctions.

Neuromuscular junctions (NMJs) are normally thought to comprise three major cell types: skeletal muscle fibres, motor neuron terminals and perisynaptic terminal Schwann cells. Here we studied a fourth population of junctional cells in mice and rats, revealed using a novel cytoskeletal antibody (2166). These cells lie outside the synaptic basal lamina but form caps over NMJs during postnatal development. NMJ-capping cells also bound rPH, HM-24, CD34 antibodies and cholera toxin B subunit. Bromodeoxyuridine incorporation indicated activation, proliferation and spread of NMJ-capping cells following denervation in adults, in advance of terminal Schwann cell sprouting. The NMJ-capping cell reaction coincided with expression of tenascin-C but was independent of this molecule because capping cells also dispersed after denervation in tenascin-C-null mutant mice. NMJ-capping cells also dispersed after local paralysis with botulinum toxin and in atrophic muscles of transgenic R6/2 mice. We conclude that NMJ-capping cells (proposed name 'kranocytes') represent a neglected, canonical cellular constituent of neuromuscular junctions where they could play a permissive role in synaptic regeneration.

Neurotoxicity of ammodytoxin a in the envenoming bites of Vipera ammodytes ammodytes.

Envenoming bites by Vipera ammodytes ammodytes (the long-nosed viper) can cause life-threatening neurotoxicity, particularly in children. We investigated the mechanisms of the neurotoxicity of ammodytoxin A, the principal toxin in the venom of these snakes, in isolated nerve-muscle preparations from mice. The toxin was bound selectively to the neuromuscular junction, and at concentrations similar to those likely to be found in the circulation of young bite victims, it blocked the response of the muscle to indirect but not direct stimulation. Electron microscopy showed that the toxin induced a small but insignificant depletion of synaptic vesicles from motor nerve terminals; nerve terminal mitochondria were swollen and damaged, but plasma membranes of terminal boutons were undamaged. Exposure to the toxin did not affect postjunctional acetylcholine receptors or cause structural damage to preterminal motor axons or muscle fibers. Spontaneous transmitter release was similarly unaffected. Taken together, these results indicate that ammodytoxin A is the principal agent involved in the neurotoxic activity of the venom of V ammodytes ammodytes and that the underlying cause of the failure of transmission may be the deenergization of the nerve terminal resulting from mitochondrial degeneration and subsequent impairment of coupling between the action-potential-induced depolarization of the nerve terminal and the evoked transmitter release.

Neuron to nerve terminals: aspects of neuropathology and toxicology

The nervous system is highly plastic. Its development and maturation is characterised by neuronal proliferation, specialisation and loss and the sorting of synaptic connectivity. Transmission (chemical and electrical), receptor and ion channel transcription and distribution all contribute to the emerging selectivity of action. Numerous factors – especially genetic and autoimmune – and extrinsic factors – synthetic and natural toxic chemicals – disrupt this process of development and maturation or interfere with the function and structure of the mature system. In this review, the response of the peripheral nervous system to such influences is discussed.